The present invention is directed to cutting inserts of a hard refractory material and a method for their fabrication.
Cemented carbide and ceramic cutting inserts are typically prepared by pressing a powder mixture in a hard steel or carbide lined steel mold at pressures ranging from 5 to 30 tons per square inch depending on the size and shape of the compact. Sintering is then performed to form the final sintered cutting tool. Typically, the steel mold or die has a raised surface area on a face which forms a chip breaker in the final sintered insert. The powder mixture includes an organic binder which strengthens the compact for holding shape during sintering. According to one technique for forming a die used in making cemented carbide cutting inserts, a copper tungsten electrode having a flat face is shaped into the desired configuration. The shaped electrode is placed adjacent the flat face of a carbide punch and the electrode configuration is burned into the punch face. The punch face is then used to produce green compacted parts.
In forming a compact, the cavity used has an inside wall conforming to the side wall configuration of desired cutting insert. For instance, a round insert would be compacted in a cylinder. The cavity includes a bottom which may be a punch or stationary flat or shaped die. The grade powder or powder mix is poured into the cavity. The top punch has a bottom surface in an appropriate configuration. Generally, the upper portion of cavity tapers outwardly, for instance at a five degree angle, to minimize interference between the punch and the side walls of the cavity. The top punch is connected to a suitable pressing device for compacting the powder.
Heretofore, typical prior processes for making shaped cutting inserts have prepared the mold of steel or carbide by laborious time consuming methods.